Physiological Origin of Biomedical Signal

7/28/2019 Physiological Origin of Biomedical Signal

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Physiological Origin of

SEB4233Biomedical Signal Processing

Biomedical Signal

Dr. Malarvili Balakrishnan

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Origin of Biomedical Signals

Human body is made up of a number of systems

e.g- respiratory, cardiovascular, nervous system, etc

Each of these systems is made up of several subsystems that

carry on many physiological processes. Each h siolo ical rocess is associated with certain t es of

signals that reflect their nature and activities.

These signals are referred as biomedical signals.

Different types ob biomedical signals:

Biochemical - hormones, neurotransmittersElectrical - potentials, currents

Mechanical - pressure, temperature

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Bioelectric signals are specific types of biomedical signals which

are obtained by electrodes that record the variations in electrical

potential generated by physiological processes.

Examples of bioelectric signals:

electrocardiogram (ECG)

electroencephalogram (EEG)

electromyogram (EMG)

electrooculogram (EOG) among others.

Observing these signals and comparing them to their known norms,

we can often detect a disease / disorders.

When such measurements are observed over a period of time, a one

dimensional time-series is obtained - this is a physiological signal

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Example:

Heart problem changes in electrocardiogram (ECG),

or changes in blood pressure

Neurological disorders (such as epilepsy)-changes in

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What is a signal

A signal is a single-valued representation of information as a

function of an independent variable (e.g., time) (Bruce, 2001).

The specific type of information being represented may have.

A signal may be a function of another variable besides time or

even a function of two or more variables.

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Commonly used Biomedical Signals

The action potential: mother of all biological signals

The electromyogram (EMG): electrical activity of the muscle

cells

The electrocardiogram (ECG): electrical activity of the heart /

cardiac cells

The electrogastogram (EGG): electrical activity of the stomach

The phonocardiogram (PCG): audio recording of the hearts

mechanical activity

The carotid pulse (CP): pressure of the carotid artery The electoretinogram (ERG): electrical activity of the retinal

cells

The electrooculogram (EOG): electrical activity of the eye

muscles6


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Action Potential (AP)

All biological signals of electrical origin are made up from

integration of many action potentials

The AP is the electrical signal that is generated by a single cellwhen it is mechanicall electricall or chemicall stimulated

It is the primary mechanism through which electrical

signals propagate between cells, tissues and organs

It is due in part, to an electrochemical imbalance across thecell membrane, and in part, due to selective permeability of

the membrane to certain ions

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Action Potential

At resting state, the cell membrane is permeable to K+ and Cl-,

but not to Na+

Lots of Na+ trapped outside make the intracellular region

electrically more negative, with a resting membrane potential

of -60 ~-80 mV

When the cell is disturbed, ion channels across the membrane

open up and allow an influx of Na+ : depolarization - inside of

the cell becomes more positive: +20mV

However, the channels close soon after, forcing the membranepotential back to its resting stage: repolarization

The change in membrane potential is the AP, which itself then

stimulates the neighboring cell, and starts the transmission of

the APs8


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Electromyogram (EMG)

The EMG is the graphic representation of the electrical activity

of the electrical activity of the muscle cells

It is the integration of millions of muscle APs as measured

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Recording EMG

EMG is a surface signal obtained through surface and/or

needle electrodes.

Usually, muscle electrical activity is recorded by placing

figure.

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Electrocardiogram (ECG)

ECG is the graphical recording of the electrical activity of the

heart.

It is the combination of many APs from different regions of the

Very commonly used signal in medical; thus reviewed

intensively

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Anatomy of Heart

Humans heart is made of powerful muscle called asMyocardium which composed of cardiac muscle fibers.

Heart anatomy is divided into four chambers which are: leftatrium, right atrium, left ventricle and right ventricle.

Two atria are thin-wall chambers used to receive blood fromveins while two ventricles are thick-wall chambers which

pump blood out of the heart.

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Anatomy of Heart

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Anatomy of Heart

The heart has four valves consist of:

Mitral valve: lies between left atrium and ventricle.

Tricuspid valve: lies between right atrium and ventricle.

Pulmonary valve: lies between right ventricle andpu monary artery.

Aortic valve: lies in the outflow tract of the left ventricle.

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The Conduction System of the Heart

The conduction system of the heart is controlled by two nodes

known as sinus node (sinusatrial or SA node) and

atrioventricular node (AV node).

The SA node is located in the right atrium at the superior vena

.

The SA nodal cells are self-excitatory known as pacemaker

cells.

Pacemaker cells generate an action potential at the rate about

70 per minute. The action potential is then propagates from SA

node throughout the atria but cannot propagate directly across

the boundary between atria and ventricles.

The AV node is located at the boundary of atria and ventricles.16


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In the normal heart, the AV node provides the propagating path

of action potential from atria to ventricles.

From AV node, the action potential propagate to the ventricles

His which named after German physician, Wilhelm His, Jr.

1893-1934.

This bundle separate into two: left and right bundle branches.

These two branches are then ramify into purkinje fibers of

ventricles. Following figure illustrate conduction system of the

heart.17


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The waveform of action potentials at different location of the

heart is shown.

The waveform of action potential at different location of the heart19


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Insight of ECG

ECG consists of waveforms that represent the polarization,

depolarization, and repolarization of the atria and ventricles of

the heart.

The waveforms are labelled as (Cheryl Passanisi, et al., 2001):

P wave: atrial depolarization

QRS complex: ventricular depolarization

T wave: ventricular repolarization

U wave: repolarization of the Purkinje fibers

Baseline: the polarized state

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Insight of ECG

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The Standard 12-Lead ECG

The ECG signal is recorded in three different electrodepositions.

Standard Limb Leads I, II, III (Bipolar Limb Leads)

Unipolar limb leads (Augmented Limb Leads)

Uni olar chest leads. a. Standard Limb Leads I II III

Each lead gives different reading.

Twelve reading is obtained where 3 from the standard leads, 3from the unipolar leads and 6 from the chest lead. (Jari Viik, etal., 2004)

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Bipolar Limb Leads:

Standard Limb Leads I, II, III

Einthoven Limb Leads and Einthovens Triangle, Malmivuo and Plonsey (1995)24


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Bipolar Limb Leads:

Standard Limb Leads I, II, III The electrode I, II and III is attached to the left arm, right arm and

the leg. Each of these leads measures voltage between two points

on the body.

Lead I: Measure the voltage between the left arm and right arm in

.

electrical activity moving in a horizontal direction.

Lead II: connects the right arm to the leg, and therefore electricity

moving down and leftward.

Lead III: Measure the voltage potential between the left arm andthe leg, thus monitor electricity moving down and rightward with

the ECG regarded as the positive pole (Jari Viik, et al., 2004).

The connection of these standard leads is known as the Eithoven

Triangle.25


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Unipolar Limb Leads

The same three leads that form the standard leads also form the

three unipolar leads known as the augmented leads.

These three leads are referred to as aVR (right arm), aVL (left

potential in the frontal plane.

These leads are unipolar in that they measure the electric

potential at one point with respect to a null point. This null

point is obtained for each lead by adding the potential from the

other two leads (Jari Viik, et al. 2004).

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Unipolar Chest Leads (Precordial Leads)

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Unipolar Chest Leads (Precordial Leads)

For measuring the potentials close to the heart, Wilson introduced

the precordial leads (chest leads) in 1944 (Jaakko Malmivvo and

Robert Plonsey. 1995).

These leads, V1-V6 are located over the left chest.

The points V1 and V2 are located at the fourth intercostal space

on the right and left side of the sternum

V4 is located in the fifth intercostals space at the midclavicular

line V3 is located between the points V2 and V4

V5 is at the same horizontal level as V4 but on the anterior

auxiliary line

V6 is at the same horizontal level as V4 but at the midline.28


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Characteristics of ECG QRS Complex:

The wave of ventricular depolarization - QRS complex, even

if not all of the components (the Q, the R, and the S) are

present.

Q wave: the first downward stroke.wave: t e rst pos t ve stro e

S wave: a negative stroke that follows a positive upstroke.

The QRS should be at least 5 mm and not more than 20 mm

tall.The width of the QRS is measured from the beginning of the

Q wave to the end of the S.

Normal QRS duration is 0.06 to 0.10 seconds, and does not

exceed 0.12 seconds30


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Characteristics of ECG

ST Segment (Welch Allyn Protocol Inc., 2003)

Begins at the J point (the point at which the QRS complex

ends and the ST segment begins).

The ST segment duration starts from the J point up to the.

Indicate the period of time between the end of ventricular

depolarization and the beginning of ventricular

repolarization.

Generally the ST segment is isoelectric, or on the baseline.

A deviation of the ST segment from the baseline (either a

depression or elevation) may be indicative of myocardial

ischemia.31


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T Wave (Welch Allyn Protocol Inc. 2003)

The wave of ventricular repolarization.

Usually deflects in the same direction as the QRS complex,

and should be smooth and rounded.e per o rom t e eg nn ng o t e wave to near y t e

end is called the relative refractory period. At this time,

the ventricles are vulnerable. A stronger than normal

stimulus could trigger depolarization.

If an R wave (ventricular depolarization) should occur

during this time, a potentially fatal arrhythmia could result.

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The baseline (isoelectric line) (Cheryl Passanisi, et al. 2001)

The resting phase of the conduction cycle, or the polarized state

The straight line on the ECG tracing, represent an absence of

electrical activity.

Important because the beginning of a waveform is marked by aepar ure or movemen away rom e ase ne.

The ending of a waveform is marked in terms of a return to the

baseline. This is critical to understand because in order to be able to

examine and measure a waveform, a clear understanding of where

the waveform begins and ends is necessary. The baseline is the reference point for determining the beginning and

end of a waveform.

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Arrhythmia

Arrhythmia: any change from the normal sequence of

electrical impulses, causing abnormal ECG (Jaakko Malmivvo

and Robert Plonsey. 1995).

Tachycardia: a heart rate of more than 100 beats per minute.

.

Arrhythmias can take place in a healthy heart and be of

minimal consequence, but they may also indicate a serious

problem and lead to heart disease, stroke or sudden cardiac

death.

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Arrhythmia

Normal

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First-Degree AV Block

Second-Degree AV Block (2:1)

Third-Degree AV Block

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Physiological Origin of Biomedical Signal